feat(invite): 好友邀请后端(注册即生效,邀请人+被邀请人各发1万金币)

- user.invite_code 列 + invite_relation 表(invitee_user_id 唯一 = 幂等防重复发奖)
- GET /api/v1/invite/me(我的码+分享链接+战绩)、POST /api/v1/invite/bind
- 复用 wallet.grant_coins 同事务发币;自邀屏蔽 / 无效码 / 新用户闸(注册72h内才发)
- alembic 迁移(11a1d08c6f55 -> invite_code_and_relation)+ 8 个测试(钱路/幂等/并发兜底全覆盖)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/main.py

@@ -22,6 +22,7 @@ from app.api.v1.compare_record import router as compare_record_router
 from app.api.v1.coupon import router as coupon_router
 from app.api.internal.price import router as internal_price_router
 from app.api.v1.feedback import router as feedback_router
+from app.api.v1.invite import router as invite_router
 from app.api.v1.meituan import router as meituan_router
 from app.api.v1.order import router as order_router
 from app.api.v1.platform import router as platform_router
@@ -79,6 +80,7 @@ def health() -> dict[str, str]:
 app.include_router(auth_router)
 app.include_router(user_router)
 app.include_router(feedback_router)
+app.include_router(invite_router)
 app.include_router(coupon_router)
 app.include_router(compare_router)
 app.include_router(compare_record_router)